1. Field of the Invention
The present invention relates generally to connectors for fiber optic cables, more specifically, to an optical connector for interconnecting multi-fiber optic cables.
2. Description of the Prior Art
The utilization of fiber optic cables or light guides, also sometimes referred to as optical communication fibers, for the transmission of information bearing light signals, is an established art. An article entitled "Fiber Optics," by Narinder S. Kapany, published in Scientific American, Vol. 203, pages, 72-81, November 1960, provides a useful background with respect to some theoretical and practical aspects of the use of fiber optic cables and connectors.
As evidenced by the preceding article, a great deal of development has been devoted to the provision of practical low-loss glass materials and production techniques for producing glass fiber cables with protective outer claddings or jackets. Presently used cables resemble bulky metallic core electrical cables and are not yet practical for use in volume and weight critical signal transmission and processing systems.
In addition to the volume and weight considerations, prior art mateable connectors that utilize either single or multiple fiber cables are subject to optical transfer losses caused by several factors including but not limited to: traverse displacements, excessive axial gap distances, axial misalignment, broken fibers, reflective losses, chips or scratched mating surfaces, and for multiple fiber bundles, low density fiber packing. Multiple fiber cable optical losses have been minimized by consolidating the fiber optic bundle to produce a closed pack array, leaving only the spaces between the adjacent fibers and the fiber cladding as lost optical area. Traverse displacements caused by excess tolerances of the contact/alignment socket fit, concentricity deviations of the contacts terminating the optic bundles, and individual fiber bundle diameter variations all result in light transmission losses. Concentricity deviations, and rotational misalignments, even when the contacts are keyed to each other, typically cause enough misalignment between fiber bundles to effectively randomize the mated fiber alignment and, thus, cause light transmission losses.
The importance of transfer efficiency cannot be under estimated and a useful overview of the subject can be found in the Bell System Technical Journal, Vol. 50, No. 10, pages 3159-3168, December 1971, specifically to an article by D. L. Bisbee, entitled, "Measurement of Loss Due to Offsets and End Separations of Optical Fibers." Another Bell System Technical Journal article of further interest appeared in Vol. 52, No. 8, pages 1439-1448, October 1973, and was entitled, "Effect of Misalignments on Coupling Efficiency on Single Mode Optic Fiber Butt Joints," by J. S. Cook, W. L. Mammel and R. J. Grow.
Transmission efficiency has had a direct bearing on the types, arrangements and selection of optic fibers and connectors for particular uses. For example, fiber Optic bundles are normally utilized only for short transmission distances in fiber optic communications networks. On the other hand, fibers are used individually as optical data channels to allow transmission over many kilometers. Some fiber optic cables utilize multi-fiber bundles due to the less stringent splicing requirements, a greater inherent redundancy, and a higher signal to noise ratio.
Multi-channel connectors typically align from two to possibly twenty fiber optic channels. These connectors can terminate both electrical and fiber optic cable simultaneously and generally utilize what is known as an electrical connector housing. Present multi-channel fiber optic connectors or fiber optic and electrical connectors are designed so that there is generally very little room within the connector housing to accommodate malfunctions associated with broken fibers which require retermination of a fiber. This difficulty is generally not a problem in electrical lines since wires generally do not crack or break. However, in fiber optic lines, if a fiber is broken it must be reterminated which generally requires removing an inch or two of a fiber. This removal in turn shortens the fiber, thereby resulting in a distorted fiber cable system.
Fiber shortening also does not lend itself to a convenient wrapping or laying of a fiber cable system at a connector cable junction. Furthermore, even if the fibers have been properly terminated so that there is no cable distortion, each one of the separate fiber optic channels must be protected and cleaned so that there will be no problems associated with the interconnection of fibers to fibers in the mated connector. In essence, what has occurred by properly protecting and isolating each one of the fiber optic contacts is that the connector has become as large as an electrical connector, thereby reducing the desirability of the use of multi-fiber optic connectors.
Another often used type of fiber optic connector is a single channel fiber optic connector. A typical single channel fiber optic connector consists of a shell for holding the fiber optic contact into position against an opposing mating fiber optic contact. This often used fiber optic connector is known as an "SMA" type of fiber optic connector. The "SMA" connector is commercially available from several companies such as Amphenol Corporation, 2122 York Road, Oak Brook, Il. 60521, and from Optical Fiber Technologies, Inc., P.O. Box 148, Nutting Lake, Mass. 01865.
The applications for single channel fiber optic connectors are primarily in areas requiring the disassembly of one channel without disturbing other channels. For example, single channel connectors are used in many industrial and commercial applications, such as building management, machine management, as well as in other communication areas where it is not desirable to have the whole communication system down when repairing just one channel.
A major disadvantage of using present art multi-channel fiber optic connector systems is that in order to repair a damaged contact, every optical contact housed in the connector must normally be reterminated. Another difficulty with multi-channel connector systems is that the termination of a cable having several fibers, requires the addition of a fiber optic contact on each one of these fibers, the polishing of each fiber, and then the fitting each fiber into a multi-channel or single channel contact. This process is very time consuming, especially if a twenty channel cable is involved. Regardless of whether a multi-channel connector or several single channel connectors must be terminated, the result is that an excessive amount of weight and physical volume is required at the connector junctions.
Heretofore, the problem of having large connectors for the termination of multi-channel fiber optic cable has been one of the detriments to the use of fiber optics. The rational being that a very small fiber optic sensor containing several fibers, also requires a large connector to properly interconnect the sensor. This dichotomy of sizes is inconsistent with the beneficial aspects of using the small fiber optic sensor. More specifically, the use of small, light weight connector assemblies on aircraft is very critical due to the space and weight design constraints that typically exist. Presently, single channel connectors, and multiple single channel connectors imply a large amount of weight, especially, when using several fiber optic cables. More particularly, within the area of an aircraft, large connector assemblies reduce the spare volume for installing other equipment due to the multitude of single channel connectors which utilize a great deal of room. Consequently, fiber optic technology is not yet convenient in weight and volume critical applications Hence, the practical use of connectors is foregone in these weight and volume critical areas, and the full benefits of fiber optic technology remains untapped.
From the foregoing, the need should be appreciated for a smaller, lighter, multi-channel, multi-fiber optic coherent bundle connector for multi-channel transmission, or what is presently called a multi-fiber single contact connector. Accordingly, a fuller understanding of the invention may be obtained by referring to the summary of the invention, and the detailed description of the preferred embodiment, in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.